The present invention relates to a rolling mill for rolling or sizing of metallic pipes, bars, or wires.
Patent document WO 98/06515 discloses a rolling mill which includes a plurality of rolling units arranged on a straight line close to one another. The rolling units are arranged exchangeably in the rolling mill. They each have three rolls which are arranged in a star-shaped configuration around a rolling mill axis. Only some rolling units, namely two last rolling units arranged at the outlet side, have rolls which are each driven from an own drive shaft. The remaining rolling units, which are provided in a substantially greater number, have each only one drive shaft which drives directly the roll shaft of each roll which has a horizontally extending rotary axis. The torque of the drive shaft is transmitted to the both other roll shafts by means of bevel gears which are arranged on all roll shafts. In order to retain the bevel gears in engagement with one another, in these rolling units a significant radial adjustment of the roll shafts and thereby of the rolls is not provided. For the both last rolling units arranged at the outlet side, the rolls can be however adjusted in a radial direction since they are driven individually and are supported radially movably.
This known rolling mill has the substantial disadvantage that the majority of the rolling units, namely those with only one drive shaft, can not be loaded sufficiently high. The reason for this is that, the roll bearings for receiving the forces and the bevel gears for transmission of the torque must be arranged within a equilateral triangle which is formed by the rotary axes of the rolls. Thereby the outer dimensions of the roll bearings and of the bevel gears are limited and as a result the magnitude of the rolling forces to be received and the torque to be transmitted are limited as well. An increase of the triangle of the rotary axis would lead to larger rolls. Larger rolls however increase the distance between the rolling units, which leads to an increase of the fraction of unusable, not measurable end portions of the rolling product. Moreover, larger rolls are more expensive in manufacture and treatment. Further, with larger rolls, higher investment cost are needed for the whole rolling mill. Therefore an increase of the triangle of the rotary axes can not be considered as an acceptable solution of the problem.
In addition to their insufficient load capability, the rolling units with only one driving shaft have the disadvantage, that with such rolling units the arrangement inside the rolling unit housing is especially expensive, since in addition to the roll bearings also the bevel gears must be accommodated inside the triangle of the rotary axes. A radial adjustment of the rolls is possible, but only with substantial structural expenses. High structural expenses without the roll adjustment lead to many components and thereby to high manufacturing and operational costs.
The expensive arrangement inside the rolling unit housing has a further disadvantage in that, the exchange of the rolls is complicated and time consuming. For this purpose it is necessary to open the rolling unit housing and to partially dismount the roll bearings as well as the bevel gears. After the roll exchange, a corresponding mounting expense is needed. For saving mounting work and time, the rolls are re-machined in the built-in condition. However, for this purpose additional special machines are required.
In the known rolling mill a substantially great part of the rolling units has each only one drive shaft and thereby the rolling mill has all disadvantages of these rolling units. The rolling mill is not sufficiently loadable, it has complicated and therefore expensive rolling units and requires a high expense for exchange and re-machining of the rolls.
In order not to put up with more disadvantages, in the known rolling mill the radial adjustability of the rolls in the rolling units with only one drive shaft and thereby in the majority of the rolling units is dispensed with. This leads in such rolling units to substantially increased costs, since in such rolling units the rolls are used up faster. In rolling units without or without sufficient radial adjustability, worn up rollers must be re-machined with a great material removal. Also with these rolling units unfavorable rolling programs require extensive material removals.